Radio receiving apparatus



Aug. 1940- L. PADDLE 2,212,182

RADIO RECEIVING APPARATUS Filed Aug. 27, 1938 Patented Aug. 20, 1940UNITED STATES RADIO RECEIVING APPARATUS Leslie Harold Paddle, England,assignor to West, Norwood, London, Telephone Manufacturing CompanyLimited, London, England Application August 2'7, 1938, Serial No.227,205

In Great Britain September 2, 1937 11 Claims. (01. 2 50-20) Thisinvention relates to electrical communication systems, and morespecifically to ultrashort wave radio systems employingsuper-regenerative receivers.

6 In receivers of this type, as is well known, a thermionic valve stagehas input signals applied to a circuit thereof the resistance of whichis made nearly zero or in some cases slightly negative, and theresistance of this circuit is then 10* cyclically varied-by means of afurther oscillation-between a slightly positive and a slightly negativevalue. The operation of the circuit is not clearly understood, but it isgenerally accepted that during the one half cycle of the furtheroscillation, which for the sake of convenience may be identified as thequenching oscillation, the circuit has a negative resistance, duringwhich time the amplitude of the input signals is building up to alimiting value determined by valve saturation and circuit conditions,during the succeeding half cycle of the quenching oscillation thestability of the circuit is restored by the resistance of the circuitbeing made positive. The output of the valve stage includes, however, asignal which is the original modulation frequency of the input signal.

While this may represent the operation of such a receiver on certainfrequencies, it is believed that on ultra-high frequencies, that isabove 30 megacycles per second, there is a secondary efiect which takesplace and modifies considerably the operation of the stage.

Since the input circuit is invariably oscillatory it follows that thebuilding up of the .voltage in the circuit to the limiting value occursgradually with each cycle of the input signal during the half cycle ofthe quenching oscillation, and it seems therefore that the circuit doesnot reach the limiting condition of saturation sufliciently rapidly todestroy the characteristic modulation; it will be apparent that nomodulation output can be obtained once this limiting value is reached.This is borne out by the observed fact that if too high a quenchingvoltage is used, causing saturation at an early point' in the quenchingcycle, the output becomes distorted.

On the other hand, when using the super regenerative receiver on ultrashort wavelengths it is believed that saturation is much more rapidlyreached and that this accounts for the fact that when a superregenerative receiver is used on these wavelengths there is a diminishedcute put whenthe input circuit is accurately tuned to theincomingsignal. It is found that there are two or more tuning points,separated from t the position of true resonance.

It is believed that in the ordinary receiver this saturation effect isnormally allowed to appear, and the system operates by virtue of a 5beat effect or heterodyne between the local quench oscillation and theinput signal, the heterodyne being demodulated within the valve toobtain the desired signal and not, as is generally supposed, the signalitself. 14)

According to the present invention, therefore, there is provided asystem which takes advantage of the true super regenerative effect onthese ultra high frequencies, and the invention consists of a receivingdevice comprising a thermionic valve, 16 means for supplying a desiredsignal to a circuit associated with said valve, the resistance of saidcircuit being low or zero,means for cyclically varying the resistance ofsaid circuit through zero, an output circuit from said valve responbsive at the frequency of the desired signal and a demodulator or thelike fed from said output circuit.

With the present invention there is provided a receiver of the type inwhich one (or more) 5 valves are employed and which are brought to thepoint of oscillation by means of an external inductance or tuned circuitoperating in conjunction with the internal capacity of the valves.Preferably two (or more) valves are employed 0 and are brought to thepoint of oscillation by the connection of an inductance between the twoanodes and a small or preferably negligible inductance between thegrids, or vice versa. Means are also incorporated whereby, through theMiller 35 effect in the valves, regeneration takes place; such means mayconsist of chokes or tuned circuits included in the cathode leads of thevalves. An oscillating voltage is also impressed upon the valve orvalves, this voltage for maximum sensi- 6 tivity being such that thecircuit operates in a super-regenerative manner, that is the circuit isalternately caused to stop and start oscillating at signal frequency inaccordance with the oscillating or quenching voltage of lower frequency.45

According to a further feature of the invention, in a receiver of thetype described, demodulation is obtained by electrodes associated withthe detector stage itself, and preferably there is 50" arranged withinthe envelope of one or both of the two valves an auxiliary anode whichoperates with the cathode to form a demodulator; moreover this auxiliaryanode is arranged with its circuit sothat the direct. current componentof its rectified output, or a part thereof, is impressed upon the gridor grids of the valves.

According to another feature of the invention, in a circuit of thisgeneral type there is employed in conjunction with the valve stage twodemodulating or rectifying devices, one of which is used to derive thedemodulation component of an applied signal and the other is used forthe purpose of controlling the grid potential in order to obtain anautomatic gain control operation.

In the accompanying drawing there are shown circuit diagrams of radioreceiving systems incorporating the present invention, 'which are givenby way of example only as indicating some of the possible forms of theinvention.

In the embodiment of the invention shown in Figure 1 use is made ofthermionic valves which are arranged in the manner disclosed-in PatentNo. 2,067,679, whereby the valves tend to oscillate. The anode-gridpaths are in series, and an inductive element is included-in the seriescircuit so formed. In this specific example use is made of two valvesV1, V2 having their anodes .joined to the terminals of an inductance L,tuned by means of a series or, as shown in Figure 1, a parallel variablecondenser C, the grids of the valves being directly-joined. The cathodesof the valves are connected through impedances, preferably chokes RFCwhich permit them to oscillate relatively in' potential. The inputcircuit, for example the aerial, is coupled by means of the mutualinductance of a coupling coil LC adjacent the anode coil L. Theregeneration which takes place in this valve stage is controlled byvariation of the anode supply voltage from battery 3 by means of aresistance R, a byepass condenser C1 beingincluded. Also included in theanode supply circuit is a means,

T cal generator OSC may be such as the secondary winding of atransformer T1, by which a quenching oscillation from a loimpressed-uponthe valve stage. Thus the valves may be brought to a condition ofincipient oscillation and then periodically brought into oscillationandnonoscillation by the'app-lication of the quench signal.

The grid circuit of the valves is completed through an impedance such asRFC and a bias ba t y B2. v

The output from the stage is obtained by means of a transformer T2arranged. between the cathodesofthe valves, the secondary winding of thetransformer, tuned to the frequency of the desired signal by condenserC3 or not, as desired, feeding a grid leak demodulator valve V3.fromwhich the modulations of the original signal are obtained by anoutput transformer T3.

It is found that, this circuit provides an excellent degree of automaticgain control, and one which is very satisfactory in operation. Forexample, it has been found possible to obtain an output constant towithin half a decibel over an input range of 26 decibels.

In the embodiment of the invention shown in Figure 2b the receivercomprises two valves which are. arranged in the manner described above,one or both of the valves having an auxiliary anode A arranged inassociation with the cathode so as to, provide a diode rectifiertherewith. v,Input is applied from a receiving aerial totheinductancearranged between the anodes 0 preferably, the received signal is appliedto a buiferj amplifier valve V4 'of'the screen grid acorn type...Fiafia, the. output of which is applied across the choke RFC connectedin the cathode lead of the valve V1.

The output from the valves V1 and V2 is applied from either the anode ofthe valves or from the grids to the auxiliary anode A, through asuitable condenser C4 if necessary, and a load resistance R1 is arrangedbetween the auxiliary anode and an earthy point of the receiver. Theauxiliary anode A may be fed from the anode of valve V2 by connectingcondenser C4 to the anode by the lead D. Whether the auxiliary anode Ais fed from the anode or the grid of valve V2, the unidirectionalvoltage produced across this resistance R1 or a part thereof is then fedback to the g ids of the valves with decoupling if necessary. Thealternating voltage appearing across the load resistance R1 andrepresenting the modulation component of the received modulated carrierwave signal is fed through a condenser 05 to the grid of a suitableamplifying valve V5 or other output circuit.

If desired, an auxiliary anode may be incorporated in each valve andpush pull demodulation used. An example of such an arrangement is shownin Figure 3. This circuit is generally similar to that shown in Figure2b except that a series tuned anode circuit is used and that thedemodulating diodes are fed from the cathodes. With this circuit the twoanodes A are joined together and the load resistance R1 is connectedbetween the anodes and earth as before. It will be remembered that thecathodes of the valves V1 and V2 are out of phase. When one anode ispositive with respect to its associated cathode (and is then passingcurrent) the other anode will be negative with respect to its associatedcathode and at that instant the anodecathode capacity of the passivediode will feed voltage to the conducting diode. At the next 1 halfcycle the position will be reversed, but the current through the loadresistance will be in the same direction at all times.

It will be appreciated that in some circumstances a direct electricalconnection exists between the auxiliary anode and one ofthe grids forexample, if the whole of the voltage across circuit may be connectedbetween the cathodes as indicated in the fragmentary circuit diagram ofFigure 4, the circuit forming the output impedance. This tuned circuitmay conveniently. consist of a parallel tuned circuit L1, C6 in serieswith two small condensers C7, C8. Such a circuit may be adjusted to givea very sharply tuned output load. Figure 4 may be used either with aseparate demodulator valve as shown in Figure 1, or with the-auxiliaryanode demodulation described with reference to Figures 2b and 3.

Figure 5 illustrates an embodiment of the present invention in whichthere is provided a valve stage comprising two triode valves V1, V2 asbefore but each valve includes two auxiliary anodes A, A1 associatedwith the cathode thereof; Two of the auxiliary anodes, one in eachvalve, are joined and are returned through a load resistance R1 to anearthy point of the cathode circuits, for example to the common, lowpotential ends of the chokes RFC included in the cathode leads. One orboth of the .second pair of anodes are connected to the grids and arealso connected, through a second load resistance R2,

to a point of the circuit negative with respect to the mean potential ofthe cathodes; for example a variable resistance R3, shunted by acondenser Cs, may be arranged between the low potential ends of thecathode chokes and the negative terminal of the high tension supply B,and the second load resistance R2 is then returned to the negativeterminal of the variable resistance.

The circuit is believed to operate in the following manner: The twovalves are brought to the point of incipient oscillation by virtue ofthe anode-grid feed-back as previously described, and the oscillation isperiodically initiated and quenched by the applied quenchingoscillations, and a highly sensitive amplifying condition is therebyproduced. When a modulated carrier wave signal is applied to the stagethe first pair of anodes serves to produce the modulation component ofthe signal, which appears across the load resistance R1 and which maybepassed to a subsequent amplifier. As with the circuit of Figure 3 thisdemodulation occurs by virtue of the fact that the cathodes operate inopposite phase, and when one anode is not passing current the capacitybetween it and its cathode serves to feed the other anode, which is thenpassing current.

The second pair of anodes is directly connected to the grids and. theseanodes operate to rectify the signal on said grids. The direct currentcomponent of rectification which appears across the associated loadresistance R2 is impressed as a bias upon the grids, so as to provideautomatic gain control. However, owing to the fact that the loadresistance is returned to a point negative with respect to the cathodesuch rectification occurs only when the signal between grids andcathodes exceeds a figure determined by the value of the negative bias.The variable resistance R3 thus affords a means by which the initialgain of the system may be controlled (as it controls the grid potential)and it also controls the delay voltage of the automatic gain controlsystem.

The second pair of anodes have been described as being directlyconnected to the grids, but if desired they may be fed from anyappropriate point of the circuit, for example from a main anode or thegrids through an isolating condenser, and the rectified voltage may beapplied from the load resistance to the grids through a decouplingcircuit.

In feeding a circu't of the type described from an open aerial it issometimes found that the aerial constants are reflected into the stage,giving rise to certain small difficulties. To overcome these, there isarranged a buffer stage consisting of a pair of acorn pentode valves V6,V1 connected in a conventional push-pull amplifier circuit, between theaerial feeder and the superregenerative stage. The valves V6, V7 are fedfrom input terminals ANT through a tuned, balanced input circuitcomprising inductances L2, L2 and tuning condenser C9. The grids of thevalves are balanced with respect to earth by condenser C It, CH) and thedirect current grid-cathode paths of the valves are completed throughresistances R4. An output inductance L3 is coupled to the tuninginductance of the valves V1, V2.

With the circuit described it has been found that the anode current isvery small--considerably less than one milliampere-and it has beenpossible to dispense with a high tension supply and to use only theapplied quenching oscillation for producing the necessary anode current.

What I claim and desire to secure by Letters Patent is:

- 1. A radio receiver comprising at least two thermionic valves eachhaving a grid and an anode electrode cooperating with a cathodeelectrode, circuit elements connecting the anode-grid paths of saidvalves in series in a circuit resonant at a desired signal frequency, aquenching oscillator circuit and a signal input circuit coupled to saidresonant circuit, impedance connected between the cathodes of saidvalves to permit the development of an oscillatory potential betweensaid cathodes, a signal frequency output circuit connected to the likeelectrodes of two valves, and a demodulator fed from said outputcircuit.

2. A radio receiving system as claimed in claim 1, wherein said outputcircuit is connected between the cathodes of the tubes.

3. A radio receiving system as claimed in claim 1, wherein said outputcircuit comprises a transformer tunable to the signal frequency andconnected between the cathodes of the tubes.

4. A radio receiving system as claimed in claim 1, wherein saiddemodulator comprises an auxiliary anode within one of said valves andcooperating with the cathode electrode thereof to form a dioderectifier.

5. A radio receiving system as claimed in claim 1, in combination withmeans for automatically varying the bias on a grid electrode inaccordance with the magnitude of the incoming signal.

6. In a super-regenerative radio receiver, a pair of thermionic valveseach including a grid electrode and an anode electrode cooperating witha cathode electrode, an auxiliary anode in at least one of said valvesand cooperating with the cathode thereof to form a diode rectifier, acircuit resonant at a desired signal frequency and including thegrid-anode paths of said valves in series, a quenching oscillatorcircuit and a signal input circuit coupled to said resonant circuit,circuit elements of high impedance at signal frequencies connectedbetween said cathodes, and an input circuit for said diode rectifierconnected to one of the electrodes of at least one of said valves.

'7. In a super-regenerative receiver, the invention as claimed in claim6, wherein said rectifier input circuit is connected to an anodeelectrode.

8. In a super-regenerative receiver, the invention as claimed in claim1, wherein said rectifier input circuit is connected to a gridelectrode.

9. In a super-regenerative receiver, the invention as claimed in claim6, wherein said rectifier input circuit is connected through saidcircuit elements to both cathodes.

10. In a super-regenerative receiver, the invention as claimed in claim6, wherein both of said valves have an auxiliary anode, and theauxiliary anodes are both connected to said rectifier input circuit.

11. In a super-regenerative receiver, the invention as claimed in claim6, wherein there is an auxiliary anode in the other valve forcooperation with the cathode thereof to form a second diode rectifier,in combination with a signal frequency output circuit for both valvesand working into said second diode rectifier, and means biasing theanode of the second diode rectifier negatively with respect to itscathode.

LESLIE HAROLD PADDLE.

CERTIFICATE OF CORRECTION.

Patent No. 2,212,182. August 20, who.

LESLIE HAROLD PADDLE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 5,seccnd column, line 514., claim 8, for the claim reference numeral read--6--; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the caseinthe Patent Office.

Signed and sealed this 1st day of October, A. D. 191w.

Henry Van Arsdale,' (Seal) Acting Commissioner of Patents.

